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Henry Jay Forman

Publications and source records attributed to Henry Jay Forman.

44 records · Page 3Linked to original sources
PubMed2002

Cellular glutathione and thiols metabolism.

Low molecular weight thiol-containing compounds have an essential role in many biochemical and pharmacological reactions due to the ease with each they are oxidized, and the rapidity with which they can be regenerated. Thioredoxin and glutathione (GSH) are two of the major small molecular weight thiol-containing compounds synthesized de novo in mammalian cells that participate in those functions. Understanding the mechanisms of thiol metabolism has special relevance to understanding the cell's defense against toxicant exposure and as the focal point in redox signaling. This commentary will, however, focus on GSH consumption and synthesis, and the role of thiols in signaling. The chemical reactions of GSH, including conjugation reactions mediated by glutathione S-transferases (GST) and oxidation reactions mediated by glutathione peroxidases will be described. The regulation of GSH synthesis will be illustrated from a compilation of studies designed to understand the various levels at which enzymatic GSH biosynthesis is controlled, and the signaling pathways that mediate them. The response of the cell to 4-hydroxynonenal (4HNE), a reactive aldehyde produced physiologically in response to inflammation and various air pollutants, will be explored in detail. Finally, the direct role of thiols as signaling molecules will be addressed, with particular attention given to "redox state." It is our aim that this commentary will lead the reader to appreciate that studies investigating the signaling for and regulation of thiol metabolism must never be generalized, and that perturbations in any of step of thiol metabolism may have etiological roles in genetically, virally, and environmentally borne pathologies.

Aldehydes↗
PubMed2002

Glutathione in defense and signaling: lessons from a small thiol.

The mechanisms of thiol metabolism and chemistry have particular relevance to both cellular defenses against toxicant exposure and to redox signaling. Here, we will focus on glutathione (GSH), the major endogenous low- molecular-weight nonprotein thiol synthesized de novo in mammalian cells. The major pathways for GSH metabolism in defense of the cell are reduction of hydroperoxides by glutathione peroxidases (GSHPx) and some peroxiredoxins, which yield glutathione disulfide (GSSG), and conjugation reactions catalyzed by glutathione-S-transferases. GSSG can be reduced to GSH by glutathione reductase, but glutathione conjugates are excreted from cells. The exoenzyme gamma-glutamyltranspeptidase (GGT) removes the glutamate from extracellular GSH, producing cysteinyl-glycine from which a dipeptidase then generates cysteine, an amino acid often limiting for de novo GSH synthesis. Synthesis of GSH from the constituent amino acids occurs in two regulated, enzymatically catalyzed steps. The signaling pathways leading to activation of the transcription factors that regulate these genes are a current area of intense investigation. The elucidation of the signaling for GSH biosynthesis in human bronchial epithelial cells in response to 4-hydroxynonenal (4HNE), an end product of lipid peroxidation, will be used as an example. GSH also participates in redox signaling through the removal of H(2)O(2), which has the properties of a second messenger, and by reversing the formation of sulfenic acid, a moiety formed by reaction of critical cysteine residues in signaling proteins with H(2)O(2). Disruption of GSH metabolism will therefore have major a impact upon function of cells in terms of both defense and normal physiology.

Aldehydes↗
PubMed2002

Priming of alveolar macrophage respiratory burst by H(2)O(2) is prevented by phosphatidylcholine-specific phospholipase C inhibitor Tricyclodecan-9-yl-xanthate (D609).

The respiratory burst in alveolar macrophages is enhanced in vitro by pre-exposure to nontoxic concentrations of hydroperoxides before stimulation by an agonist, which may represent a feed-forward regulatory mechanism. Tricyclodecan-9-yl-xanthate (D609), an inhibitor of phosphatidylcholine-specific phospholipase C (PC-PLC), suppresses this priming of the respiratory burst by pre-exposure to H(2)O(2) in NR8383 alveolar macrophages (up to 100 microM D609, 400 nmol of H(2)O(2) added to 5 x 10(6) cells 15 min before stimulation with ADP). D609 has potential as an antioxidant due to its dithiocarbonate functional group that allows it to slowly react with H(2)O(2) and rapidly reduce cytochrome c, which interferes with a common assay for the respiratory burst. Nonetheless, the antioxidant properties of D609 do not account for its inhibition of priming of the respiratory burst by H(2)O(2). Reduction of nitro blue tetrazolium is the basis for an assay for superoxide production with which D609 does not interfere. With this assay, it was found that D609 does not inhibit the respiratory burst per se, but prevents its enhancement by pre-exposure to H(2)O(2). Consistent with a role of diacylglycerol generation by phospholipase C, this enhancement was mimicked by pre-exposure to phorbol ester. In contrast with priming, receptor-mediated stimulation of the respiratory burst depends on the better characterized phosphatidylinositol-specific phospholipase C. Priming of the respiratory burst by H(2)O(2) joins the list of inflammatory responses that are inhibited by D609. Nevertheless, the results herein indicate that caution should be exercised in the interpretation of the effects of D609 to consider both antioxidant effects and inhibition of PC-PLC.

Animals↗
PubMed2002

A549 subclones demonstrate heterogeneity in toxicological sensitivity and antioxidant profile.

In A549 cell culture, significant variability was found in sensitivity to actinomycin D. Using limiting dilution, actinomycin D-susceptible (G4S) and -resistant (D3R) subclones were isolated. G4S cells were also susceptible to protein synthesis inhibitors, a redox cycling quinone, and an electrophile with concomitant activation of caspases 3 and 9. D3R cells were resistant to these agents without caspase activation. Antioxidant profiles revealed that D3R cells had significantly higher glutathione and glutathione reductase activity but markedly lower catalase, glutathione peroxidase, and aldehyde reductase activities than G4S cells. Thus A549 cells contain at least two distinct subpopulations with respect to predisposition to cell death and antioxidant profile. Because sensitivities to agents and the antioxidant profile were inconsistent, mechanisms independent of antioxidants, including the apparent inability to activate caspases in D3R cells, may play an important role. Regardless, the results suggest that antioxidant profiles of asymmetrical cell populations cannot predict sensitivity to oxidants and warn that the use of single subclones is advisable for mechanistic studies using A549 or other unstable cell lines.

Adenocarcinoma↗
PubMed2002

Macrophage signaling and respiratory burst.

Macrophages are key defenders of the lung and play an essential role in mediating the inflammatory response. Critical to this is the activation of the NADPH oxidase. Through receptor-mediated interactions, extracellular stimuli activate pathways that signal for the phosphorylation and assembly of the NADPH oxidase. Once the NADPH oxidase is activated, it produces superoxide and H2O2 in a process known as the respiratory burst. The involvement of O2.- and H2O2 in the antimicrobicidal function of macrophages has been assumed for many years, but it is now clear that the H2O2 produced by the respiratory burst functions as a second messenger and activates major signaling pathways in the alveolar macrophage. Both the nuclear factor-kappaB and activator protein-1 transcription factors are activated by H2O2 produced by the respiratory burst, and, since these control the inducible expression of genes whose products are part of the inflammatory response, this may be a critical link between the respiratory burst and other inflammatory responses. The c-Jun N-terminal kinase (JNK) and extracellular-regulated kinase (ERK) pathways, two members of the mitogen-activated protein kinase family, are also activated by the respiratory burst. JNK is activated by both exogenous and endogenously produced H2O2. Studies with ERK have shown that specific agonists of the respiratory burst, but not bolus H2O2, can activate this pathway. The ERK pathway also modulates the expression of genes via phosphorylation of the transcription factor Elk-1 that controls the production of the c-Fos transcription factor. Although an understanding of the mechanism of redox signaling is in its infancy, it is becoming clear that the reactive oxygen species produced by the respiratory burst have a profound effect on intracellular signaling pathways and ultimately in modulating gene expression.

Animals↗
PubMedDate not supplied

HNE--signaling pathways leading to its elimination.

The oxidation of polyunsaturated fatty acids results in the production of HNE, which can react through both non-enzymatic and enzyme catalyzed reactions to modify a number of cellular components, including proteins and DNA. Multiple pathways for its enzyme catalyzed elimination include oxidation of the aldehyde to a carboxylic acid, reduction of the aldehyde to an alcohol, and conjugation of the carbon-carbon double bond to glutathione (GSH). Interestingly, the enzymes that result in HNE elimination are induced by HNE itself although the chemical mechanism for signaling is not well understood. One of the striking effects of HNE is that after a transient decrease in GSH, synthesis of GSH is elevated through induction of glutamate cysteine ligase (GCL), which catalyzes the first step in de novo synthesis of GSH. GCL has two subunits, which are transcriptionally regulated by a wide variety of agents, including oxidants and electrophiles, such as HNE, which elevates both. The transcriptional regulation of GCL has been the subject of many investigations yielding a complex picture in which the pathways for up-regulation of the subunits appear to be independent and vary with inducing agent and cell type. We have found that in human bronchial epithelial cells, HNE acts through AP-1 activation with signaling through the JNK pathway, and that neither the ERK nor p38(MAPK) pathways is involved. With these results we review what is currently known about the signaling mechanisms for removal of HNE, focusing principally on conjugation mechanisms involving GSH.

Aldehydes↗
PubMedDate not supplied

Redox signaling.

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) have recently been shown to be involved in a multiplicity of physiological responses through modulation of signaling pathways. Some of the specific signaling components altered by reactive oxygen and nitrogen species (RONS) have begun to be identified. We will discuss RONS signaling by detailing the chemistry of signaling, the roles of antioxidant enzymes as signaling components, thiol chemistry in the specificity of RONS signaling, .NO-heme interactions, and some do's and don'ts of redox signal research. The principal points raised are that: (1) as with classic signaling pathways, signaling by RONS is regulated; (2) antioxidant enzymes are essential 'turn-off components in signaling; (3) spatial relationships are probably more important in RONS signaling than the overall 'redox state' of the cell; (4) deprotonation of cysteines to form the thiolate, which can react with RONS, occurs in specific protein sites providing specificity in signaling; (5) although multiple chemical mechanisms exist for producing nitrosothiols, their formation in vivo remains unclear; and (6) caution should be taken in the use of 'antioxidants' in signal transduction.

Animals↗